EventHandlers.cs

    public class ProductAddedEventHandler: INotificationHandler<ProductAddedEvent>
    {
        private readonly IProductReadModelRepository _repo;

        public ProductAddedEventHandler(IProductReadModelRepository repo)
        {
            _repo = repo;
        }

        public void Handle(ProductAddedEvent @event)
        {
            var product = new ProductReadModel(@event);
            _repo.Insert(product);
        }
    }

    public class ReviewAddedEventHandler : INotificationHandler<ReviewAddedEvent>
    {
        private readonly IProductReadModelRepository _repo;

        public ReviewAddedEventHandler(IProductReadModelRepository repo)
        {
            _repo = repo;
        }

        public void Handle(ReviewAddedEvent @event)
        {
            var product = _repo.Find(@event.ProductId);
            product.Apply(@event);
            _repo.Update(product);
        }
    }

    public class OrderCompletedEventHandler : INotificationHandler<OrderCompletedEvent>
    {
        private readonly IProductReadModelRepository _repo;

        public OrderCompletedEventHandler(IProductReadModelRepository repo)
        {
            _repo = repo;
        }

        public void Handle(OrderCompletedEvent @event)
        {
            var product = _repo.Find(@event.ProductId);
            product.Apply(@event);
            _repo.Update(product);
        }
    }

    public class FieldValueChangedEventHandler : INotificationHandler<FieldValueChangedEvent>
    {
        private readonly IProductReadModelRepository _repo;

        public FieldValueChangedEventHandler(IProductReadModelRepository repo)
        {
            _repo = repo;
        }

        public void Handle(FieldValueChangedEvent @event)
        {
            var product = _repo.Find(@event.ProductId);
            product.Apply(@event);
            _repo.Update(product);
        }
    }